1. Field of the Invention
The present invention relates to a driving force transmission apparatus that transmits a driving force between rotating members.
2. Description of Related Art
Driving force transmission apparatuses are known which are used, for example, for a driving force transmission system in a vehicle and which enable connection and disconnection of transmission of a driving force between rotating members. See, for example, International Publication No. WO 2005/106272.
A clutch apparatus described in International Publication No. WO 2005/106272 is used for a speed change gear in a vehicle and includes a first frictional disc engaged with an outer peripheral surface of a shaft-like clutch hub in a splined manner, a second frictional disc engaged with a cylindrical clutch drum in a splined manner, an electric motor that generates mechanical power pressing the first frictional disc and the second frictional disc against each other, and a lock mechanism that allows the pressing force to be maintained between the first frictional disc and the second frictional disc while current supply to the electric motor is blocked. The mechanical power of the electric motor is decelerated by a speed reduction mechanism and converted into linear motion by a cam mechanism to actuate the lock mechanism.
The second embodiment in International Publication No. WO 2005/106272 (see FIG. 11) describes a cylindrical latch mechanism used as the lock mechanism, which has a first internal cylinder with a switching slope, an external cylinder with shallow grooves and deep grooves alternately arranged in a circumferential direction as positioning grooves, and a second internal cylinder with a moving pin. In the cylindrical latch mechanism, the switching slope of the first internal cylinder allows the moving pin on the second internal cylinder to move between the shallow groove and the deep groove in the external cylinder, enabling switching between a lock state where the moving pin is held in the shallow groove and an unlock state where the moving pin is held in the deep groove.
Enhanced performance of recent vehicles contributes to improved interior silence, with the result that a user such as a driver is likely to hear an operating sound of the driving force transmission apparatus. This tendency is significant, for example, in vehicles including the electric motor as a driving source. The operating sound may be abnormal sound or noise to occupants, who may thus feel unpleasant. Consequently, further improvement of the silence of the driving force transmission apparatus has been demanded.
However, when the cylindrical latch mechanism described in International Publication No. WO 2005/106272 is used, collision sound is generated, during operation of the cylindrical latch mechanism, by collisions between the moving pin on the second internal cylinder and bottom surfaces of the positioning grooves in the external cylinder. The collision sound may be heard by the user.